When you encounter the error message "InnoDB: Error: log file ./ib_logfile0 is of different size" after modifying MySQL's InnoDB configuration, it indicates a mismatch between your configured log file size and the existing log files. This typically occurs when you:

• Modify innodb_log_file_size in my.cnf/my.ini
• Have existing ib_logfile0 and ib_logfile1 in your MySQL data directory
• Attempt to restart MySQL server

InnoDB maintains transactional consistency through its redo log files (ib_logfile0 and ib_logfile1). These files are created during MySQL initialization with default settings. When you later change the log file size in configuration:

innodb_log_file_size = 256M

MySQL cannot simply resize these files on the fly - they're critical to the ACID compliance of the database. The engine requires both log files to have identical sizes for proper operation.

To properly implement your new InnoDB log file size:

1. Stop MySQL service:

   sudo systemctl stop mysql

2. Backup your data (critical step):

   sudo cp -a /var/lib/mysql /var/lib/mysql_backup

3. Remove existing log files:

   sudo rm /var/lib/mysql/ib_logfile*

4. Verify your configuration in my.cnf:

   [mysqld]
   innodb_buffer_pool_size = 2560M
   innodb_log_file_size = 256M
   innodb_log_buffer_size = 8M
   # Other InnoDB parameters...

5. Start MySQL:

   sudo systemctl start mysql

When working with InnoDB log files:

• For high-write systems, consider larger log files (up to 512MB)
• Always maintain identical sizes for both log files
• The total log file size (log_file_size × 2) should be about 1-2 hours of your peak write workload

Example calculation for a busy e-commerce database:

innodb_log_file_size = 512M  # For ~1M transactions/hour
innodb_flush_log_at_trx_commit = 2  # Balanced durability/performance

If you still encounter issues:

• Check file permissions: sudo chown -R mysql:mysql /var/lib/mysql
• Verify disk space: df -h /var/lib/mysql
• Inspect MySQL error log: sudo tail -50 /var/log/mysql/error.log

When configuring InnoDB parameters in MySQL, one common pitfall is encountering the error:

InnoDB: Error: log file ./ib_logfile0 is of different size 0 5242880 bytes
InnoDB: than specified in the .cnf file 0 268435456 bytes!

This occurs when you modify innodb_log_file_size in your configuration but existing log files don't match the new specification.

InnoDB maintains transaction logs (ib_logfile0 and ib_logfile1) that must be of identical size. The default size is typically 5MB (5242880 bytes). When you change this value in my.cnf, MySQL expects to find log files matching the new size.

The error appears because:

• Existing log files were created with default size (5MB)
• New configuration specifies different size (256MB in this case)
• MySQL refuses to start with this mismatch for data integrity

To properly configure innodb_log_file_size, follow these steps:

# 1. Stop MySQL service
sudo systemctl stop mysql

# 2. Backup existing log files (optional but recommended)
sudo cp /var/lib/mysql/ib_logfile{0,1} ~/mysql-backups/

# 3. Remove existing log files
sudo rm /var/lib/mysql/ib_logfile{0,1}

# 4. Modify my.cnf with new settings
sudo nano /etc/mysql/my.cnf

Your InnoDB configuration should include:

[mysqld]
innodb_buffer_pool_size = 2560M
innodb_log_file_size = 256M
innodb_log_buffer_size = 8M
innodb_flush_log_at_trx_commit = 2
innodb_thread_concurrency = 16
innodb_flush_method = O_DIRECT

Then restart MySQL:

sudo systemctl start mysql

When adjusting InnoDB log file size:

• Larger sizes improve performance for write-intensive workloads
• Smaller sizes reduce recovery time after crashes
• Recommended size is typically between 128MB-2GB for most production systems
• The total combined size shouldn't exceed innodb_buffer_pool_size / 4

If issues persist:

# Check MySQL error log
sudo tail -100 /var/log/mysql/error.log

# Verify file permissions
sudo ls -la /var/lib/mysql/ib_logfile*

# Check available disk space
df -h

Remember that any changes to innodb_log_file_size require removing the existing log files, as MySQL won't automatically resize them.